1. Field of the Invention
This invention relates generally to resonators, and more particularly, to a device that both actuates and senses structural or acoustic vibrations within a housing.
2. Discussion
Many possible applications exist in which it is desirable to create a sustained resonance of a structural or acoustic mode of vibration. In one such application, in a personal paging device, it is desirable to create structural vibrations to produce a tactile alert, or radiated sound waves to produce an audible alert. In another application, it is desirable to generate sound waves from the resonance of a car or truck panel and use the sound waves as a horn for the car or truck. In, still other applications, it is desirable to generate a sustained resonance of a structural mode of vibration either in a resonant ring or inchworm motor for producing large relative translational or rotational motions through a series of small vibratory steps, or in an integral compressor in a refrigeration system by producing compression waves in an acoustic cavity through an induced vibration of a flexure mechanism.
In all of the above applications, the sustained resonance of either a structural or an acoustic mode of vibration within a structure can be achieved by driving a mechanism, such as an actuator, integrally attached to the structure to create the vibration. To create the vibration in an efficient manner, the actuator should be driven at a frequency coinciding with the natural resonance frequency of the target structural or acoustic mode of vibration. Driving the actuator at this natural frequency takes advantage of the natural dynamic amplification factor Q of the resonance by producing, from the given actuator input, a motion greater in amplitude than if the driving mechanism was driven in an off-resonant condition.
In the past, typical mechanically-tuned excitation devices have been used for various of the above applications. With such devices, a fixed sinusoidal signal, pretuned to coincide as closely as possible with the natural resonance frequency of the particular structure, is input into the structure. However, such mechanically-tuned devices are prone to errors due to manufacturing tolerances in the devices themselves. Further, these devices are limited in effectiveness due to various uncertainties such as temperature and humidity, which may affect stiffness and mass properties in the device. In addition, as the systems in which the vibratory devices are implemented change over time due to fatigue, creep and microcracking, the devices become less accurate. Also, the drive frequency of such devices often drifts due to the effect of varying temperatures on the electronic components of the devices. While many of these devices could be adjusted to compensate for the above conditions, typical vibratory devices have no means for automatically adjusting the excitation frequency to correspond to the target resonance frequency of the structures in which the devices are implemented.
In view of the above, what is needed then is a device that actuates structural or acoustic vibrations in real time, and senses these vibrations to insure that the excitation frequency coincides with the target resonance frequency at all times, thus maximizing efficiency in generating an induced vibration.